Sound-reproduction apparatus



Jan. 3, 1928.

c. J. MORTON SOUND REPRODUCTION APPARATUS Filed May 1'7 1925 I )1 l5 l9 Inventor":

Cecil J. Morton,

bg @MW His Attorneg.

Patented Jan. 3, 1928..

UNITED STATES 1,655,283 PATENT OFFICE.

CECIL J'. MORTON, F COVENTRY, ENGLAND, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SOUND-REPRODUCTION APPARATUS.

Application filed May 17, 1926} Serial No. 109,654, and in Great Britain June 12, 1925.

This invention relates to sound reproducing instruments, such as telephone receivers or loud speakers, (which instruments, as is well known in the art, will also serve as sound transmitters, i. e., to convert sound waves into corresponding electric oscillations) and has for its object the provision of an instrument of simple design which will reproduce sound faithfully.

In one well known type of such instruments the diaphragm is formed of magnetic material and is located in a magnetic field, the fiux of which is varied in accordance with the electric oscillations received in opcrating coils. In another well known type a magnetic reed, which may be flexibly or pivotally supported, is adapted to be vibrated responsively to receive electric oscillations and is connected to transmit its vibrations to a dia hragm.

In contra distinction to these known arrangements, according to one feature of the present invention, a plunger of magnetic ma terial is axially vibratable in a magnetic field within the sphere of influence of an operating coil.

According to another aspect of the invention a magnetic plunger is vibrated within the sphere of influence of a coaxially ar ranged operating coil which is located adjacent to one of the poles of a magnetic circuit.

The plunger may be formed integrally with a diaphragm, but preferably it is secured thereto in any suitable way, as by a 5 screw, rivet or the like. This latter arrangement has the advantage that the diaphragm itself need not be made of magnetic material.

The invention further comprises the com bination of a pot-shaped magnet with a magnetic plunger located within an operating coil. The term pot-shaped is used to denote the type of magnet which has a central limb within a surrounding shell, tube, cup

or open-work cage, the central limb being connected at one end to the surrounding shell and having an air gap left adjacent to its other end. Such a magnet may be excited when in use by direct current, or alternatively, it may include one or more permanent ma nets in its structure. For instance, the outs1de shell may be a single ring magnet 1or a battery of bar magnets of cobalt steep A construction according to the present invention involves the use of a central limb which dpes not extend the whole length of the magnetic structure, and the operating coil is fixed upon the face of this limb.

With this construction a further feature of the invention consists in the use of a magnetic shunt between the central limb and the surrounding shell, which is formed by an annular extension on the central limb and around the operating coil. The object of this magnetic shunt is to provide a high permeability magnetic path for the varying flux produced by the actuating coil.

Any suitable type of instrument casing may be used, which preferably includes means for adjusting the magnetic structure toward or away from the plunger.

It has been found that a small coil is sufficient and this feature assists in reducing manufacturing cost. Another advantage in arrangements according to the invention resides in the small dimensions of the magnetic plunger, in which the flux variations occur, with, the resultant reduction of the hysteresis loss.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, will best be understood from reference to the following specification taken in connection with the accompanying drawing, in which the figure shows in vertical cross section a construction embodying the features of my invention.

The instrument here shown comprises a casing 11 which may be formed of cast iron or other suitable material and which has fastened to it the cover plate 12 provided with an opening 13 for receiving the end of the sound horn. The diaphragm 14 may have its periphery embedded in a sheet of india rubber 15 and clamped between the cover plate 12 and the casing 11, as shown. The magnet assembly is located in the hollowed out portion 16 of the casing and is arranged to be operable toward or 'awa from the diaphragm by means of the nut 14 swivelled in the opening 18 in the casing and having threaded engagement with the stem of the bolt 19 secured to the magnet 105 assembly.

The magnet assembly com rises an annular or rin magnet 21, pre erably of co balt steel, w ich 1s magnetically connected at its lower end with the magnetic disk 22 and at its upper end with theannular member 23 of magnetic material. Secured cen trally to the disk 22 is a central pole piece 24, which. is here shown as being clamped by means of the bolt 19. The upper end of the central pole 2a is enlarged to form a recess as shown at 25 and provided with an upwardly extending annular rim 26, the end of which terminates just short of the underside of the annular member 23. An annular operating coil 27 is looated'within the rim 26 at the'end of thecentralpole piece andthe whole magnet assembly ismounted in the cup shaped member 28 which maybe made of aluminumiandwhichis provided with a longitudinal groove 29 engagedby the screw 31 in the casing 11, whereby rotation of the magnet assembly is prevented.

When the instrument is used as a loud sfpeaker, operation-of: the diaphragm,is efected by means of themagnetic plunger 32 which is here shown as secured'by'ascrew to thediaphragmand which passes through the opening in the annular member 23.-andteminates adjacent the end of the central core 24. It will readilybe-understood that, when the operating coil'27 isenergized by fluctuating electriccurrents corresponding-to. the impressed Isoundwaves, the plunger will alternately be drawn further towards" or forced away; from the central pole piece, thus vibrating the diaphragm in. accordance with the impressed oscillations;

The upwardly extending rim 26 forms an annular shunt for the fluctuating fltrx'produced-by an oscillating current'in the operating coil 27.

What 1' claim as new" and desire to secure by Letters Patent of the United Statesis:

1. In an apparatus for sound reproduction, a core'having its end recessedto form a'magnetic shunt, a diaphragm adaptedto be vibrated, a plunger of: magnetic material attached thereto, a stationary annular coil mounted in said recess and adapted to actu-.-

ate said diaphragm, saidplunger being'axially movable within said coil.

2. In an apparatus'for sound reproduction,

a core having its endrecessedlto form amage neticshunt, asub'stantially flat diaphragm,

a, plunger; of magnetic material securedthereto, a; stationary coil mounted in said recess. and surrounding said plunger for.

newness actuating said diaphragm, said plunger being movableaxially within said coil.

3. In an apparatus for sound reproduction, a core having its endrecessed toform a magnetic shunt, a vibrating diaphragm, a plunger of: magnetic material atttached thereto, a stationary annular coil mounted in said recess'and adapted to actuate said diaphragm, said plunger being axially movable within a magnetic field produced by said coil, and means for adjusting the position of said core with respect to said plunger.

4. Aringshaped: erm'anent magnet, magnetic disks cooperating with each end of said magnet, one of said disks being provided with a central opening, a pole piece located centrally within the permanent magnet, said pole piece having a recessed portion adjacent said central opening, a coil located in the recessed portion, a diaphragm, and a magnetic plunger mounted. on the diaphragm and movable axially within said central. opening and" said coil.

5. In an apparatus for sound reproduction, a diaphragm, a magnetic plunger attachedethereto, apermanent magnet substantially U shaped in vertical cross section, a magnetic disk mounted on saidpermanent magnet and havingacentral opening, a pole piece positioned centrally within said permanentmagnet, said pole piece having a I'QCGSSGdPOI'tlOIl, an annular coil within said recessedportion, said coil having an opening in alignment withthetopening in said disk, said plunger being axially movable within the openings ofsaid disk and coil.

6. In an apparatusfor sound reproduction, a diaphragm, a plunger of magnetic material attached thereto, a ermanent magnet cooperating with' said iaphragm, said magnet being substantially U shaped in vertical cross section, a magnetic disk' mounted onthe open end'of said magnet, said disk having a. central 0 ening, apole piece positioned centrall wit in said magnet and-beneath'said disk, said pole piece having a recessedportion at one end thereof.

and a coil within said recessed portion adapted to operate said plunger tovibrate said diaphragm.

In witness whereof, I have hereunto set my hand this twenty-seventh day of April,

CECIL J, MORTON. 

